Terminal for resistors



Aug. 28, 1934.

M. BJORNDA-L TERMINAL FOR RESISTORS Filed Oct. 28, 1929 INVENTOR ATTO Patented Aug. 28, 1934 PATENT OFFICE 1,971,809 TERMINAL FOR RESISTORS Magnus Bjorndal, Jersey City,

Hardwick, Hindle, In

N. J., assignor to 0., Newark, N. J., a corporation of New Jersey Application October 28,

1 Claim.

This invention relates to terminals or contacts for resistance units of the type consisting of a tubular member upon which is wound a wire of the desired resistance embedded in vitreous enamel or other suitable insulating material.

One of the most important factors in the manufacture of such resistors is the method of making contact between the ends of the wire and the terminals by which the resistor is connected in the circuit in which it is to be used. It is of course highly desirable that the resistance at these points he reduced to a minimum. Soldering, welding or brazing give good electrical connections but have several practical and economic disadvantages. Soldering cannot be used in the case of resistors having vitreous enamel coverings of relatively high melting points as compared withthat of the solder. While brazing and welding may be done at temperatures considerably above the fusing point of the enamel, there is danger of burning the wires because they easily oxidize and become brittle near the joints. These methods also require experienced labor which adds to the cost of production of the resistors.

In the mass production of resistors for small capacities, using extremely fine wires, it has been found that a direct contact between wire and terminal, made'un'der pressure to prevent oxidation and keep the enamel out,-is the most satisfactory solution. However,- there are many ways of doing this, but only a few of them are effective. In most designs'there are tabs or tongues cut out of the copper te'rminala'nd around which the ,wire is fastened and clamped down. Unfortunately these tabs always have two or more sharp edges around which the wire is wound, so that no matter how hard the tab is force'd'down the enamel will flow in and insulate the wire from the terminal except at the sharp comers.-

the wire and especially the copper of the terminal will oxidize slightly at the points-of contact and this will add tothe contact resistance. In the firing process the entire length of the resistance wire will oxidize slightly and through this almost infinitesimal reduction in cross section there will be a noticeable rise in resistance which will vary with the temperature applied. This rise in resistance usually amounts to only one or two percent, but it has been found that faulty designed contacts increase the resistance by another five or six percent.

The heat generated at the contact joint in addition to that from the resistance may be enough to slowly oxidize and corrode the contact to such a degree that an open circuit will ultimately re- In the enameling process 1929, Serial No. 402,955

sult. A reduction of this contact resistance means a reduction of the heat generated and a longer life of the unit. This reduction can only be obtained by increasing the area of the contact surface between the wire and the terminal.

It is an object of this invention to provide a terminal for a resistor which avoids the objections recited above and can be easily and cheaply produced and assembled with the other elements of the resistor.

In accordance with the invention the terminal consists of a conducting strip adapted to be bent around the tubular member of the resistor and fastened in place by means inherent in the terminal and which when effective do not protrude beyond its sides. Contact between the terminal and the wire of the resistor is obtained by means of a specially shaped eyelet produced during the formation of the terminal and about which the end of the wire is wound when the terminal is in place on the resistor so that when the eyelet is pressed down contact will be made with the end of the wire for a considerable distance.

A clean contact is thus assured'because the enamel will not fiow in between the wire and the part of the eyelet with which it is in intimate contact. The end of the wire is bent on a definite radius which prevents it from receiving any mechanical injuries as frequently happens when the wire is attached to sharp bends.

The particular nature of the invention as well as other objects' and advantages thereof will appear more clearly from a description of a preferred embodiment as shown ing drawing .in which Fig. 1 is a side view of a resistor provided with the terminals of the invention,

Fig. 2 is an end view of the resistor,

Fig. 3 is a plan view of the condition,

Fig. 4 is a view of a portion of the terminal on an enlarged scale to show more clearly the formation of the eyelet,

Fig. 5 is a similar view showing the eyelet in flattened condition,

Fig. 6 is a view like that of Fig. 5 but taken in transverse section through the resistor and the terminal thereon along the line 66 of Fig. 7, and

Fig. 7 is an enlarged plan view of the eyelet in flattened condition.

The resistor consists of a tubular member 1 formed of suitable insulating material upon which is wound a wire 2 of sufficient size and a tab on the terminal by in the accompanyterminal in a flat length to give the required carrying capacity and resistance for the circuit in which it is to be used. Eachterminal 3 of the resistor consists of a strip a of conducting material cut to suitable size the rest of it as indicated at 5. A tab 6 projects from one edge of the strip and is adapted to be bent to fit in a notch 7 at the end of the member 1 when the terminal is in place thereon to prevent it from turning. A pair of tabs 8 project from opposite edges of the strip with their free edges extending slightly within the edges as indicated at 9. All the tabs are most conveniently formed by a swedging operation.

when the strip is bent around the member 1 the tabs 8 are bent over the end 5 to hold'the terminal firmly in place. By forming the tabs with their edges extending slightly within the strip they do not project beyond the edges when in final position as shown most clearly in Fig. 1. This permits the wire to be wound close to the terminal which is especially advantageous in the case of small resistors. The extended end 10 of the strip has a hole 11 and a recess 12 for attaching the resistor and connecting it in circuit.

For the purpose of attaching the ends of the wire tothe terminals each strip is provided with an eyelet 13 of novel shape. It is formed by piercing the strip with a polygonal punch having sharp edges and a fine point. The resulting parts 1.4 surround a substantially polygonal aperture and are drawn out into petal-like shape by the movement of the punch in a circular die, the piercing and drawing all being done in the same operation. As a result of this operation the outer surface of the shank of the eyelet is of substantially cylindrical form although the aperture in the strip is polygonal. As shown herein the aperture is square and there are four petals, but it will be understood that it may be of any other contour with corresponding number of petals surrounding it. The end of the wire is wound about the shank of the eyelet as shown most clearly in Fig. '7, after which the petals are pressed downwardly and outwardly against the strip to bind the end of the wire firmly in place and provide a good electrical contact between it and the strip as shown most clearly in Fig. 6.

The use of the split eyelet results in important and shape. One end of the strip is narrower thanadvantages over one of ordinary continuous form. In the case of the'latter the section of the strip where it is located will be so stiff that when it is bent around the tube of the resistor there will be a little bump on each side of the eyelet which will later straighten out when the eyelet is hammered down. This tends to loosen the terminal on the resistor and when the latter goes through the furnace during thecoating operation the terminal may become displacedand the resistor has to be discarded. By splittiii'x the eyelet the strip may be bent closely around the tube of the resistor at all points so that the'condition described above will not exist.

When the eyelet is split its petals separate as it is bent around the tube of the resistor so that the wire may be wound about the shank of the eyelet without any danger of its slipp n off over the end of the eyelet before the petals of the latter can be bent down.

The final operation in the manufacture of the resistor is the coating of the tubular member 1, the wire 2 and the bent portions of the terminals 3 by suitable material, such as vitreous enamel, leaving the extended ends 10 of the terminals exposed for attachment to suitable fastening devices of the apparatus in which the resistor is to be used and for the purpose of permitting external wires to be soldered otherwise connected thereto. ,105

While a preferred embodiment of the invention has been shown and described herein, it will be understood that various changes in the details of construction may be made without de= parting from the principle of the invention can) defined in the appended claim.

I claim:-

A terminal for a resistor of the type having a member upon which a wire is wound, consisting of a strip of conducting material adapted to be bent around the member, said strip being provided with a tab extending from one side of the strip and adapted when the strip is bent around the member to fit within a recess in the end of the member, means associated with the strip for holding it in place on the member and means for attaching the wire of the resistor to the terminal.

GNUS BJORNDAL 

